Rinse agents have been used in household and institutional warewashing for many years. Commonly rinse aids provide an effective amount of a sheeting agent or rinse aid to ensure that the surface tension of the aqueous rinse is reduced and sheeting is promoted to prevent the formation of water beads that can dry into water spots and streaks. Nonionic surfactants used in conventional rinse aids are polyalkylene oxide polymers made from ethylene oxide and propylene oxide, (block or heteric polymers thereof). For example, Altenschopher, U.S. Pat. No. 3,592,774 issued Jul. 13, 1971 discloses a rinse aid concentrate which may be dispensed during a rinse cycle by automatic dosing. Optionally, the concentrate may also contain anionic surfactant or a water soluble organic solvent. J. Diamond et al, U.S. Pat. No. 3,272,899 discloses a solid block pellet or bar of wetting agent which may be positioned in a stream of rinse water to provide a gradual dissolution of the wetting agent into the rinse. The solid wetting agent can contain a nonionic surfactant and 3-20% of an alkyl substituted amide. Smith et al, U.S. Pat. No. 4,545,917 discloses a water soluble solid composition useful in rinsing comprising one or more polyethylene glycol having a molecular weight of at least 4,000 and a nonionic surfactant composed of a C.sub.8-18 ethoxylated straight chain alcohol, a solid C.sub.10-24 fatty acid alkanol amide and a nonionic amine of polyglycol condensate.
Solid rinse aids are available for household and institutional warewashing. In household machines, rinse aids are generally packaged in a container or basket introduced into the internal washing compartment of a machine. Water used in the rinse cycle dissolves portions of the rinse aid which enters the rinse water. Institutional machines are generally either low temperature machines (water temperature 120.degree.-140.degree. F.) or high temperature machines (temperature 160.degree.-180.degree. F.). Low temperature machines can avoid high costs associated with heating water and are often more convenient for dispensing rinse aids into a machine sump. In high temperature systems, dissolved rinse aid is often injected into a rinse water line prior to entering the machine through a stationary or rotary spray arm. A continuous stream of hot water is commonly provided through the spray arm for rinsing. Consequently, a rinse aid for use at high temperature systems must be dispensed into and sufficiently dissolved in the hot water system to permit successful injection of the material into a high temperature spray arm. Such high temperature machines are generally more complex and high volume.
The wetting or sheeting agents used in the invention should be soluble or capable of being solubilized. Useful concentrations of the material should produce little or no foam, even in the presence of compositions, such as residual protein, that generate foam. Lastly, the agent should reduce surface tension and promote sheeting and drainage of rinse water off the ware. In addition to the need for low foaming, soluble surfactants providing anti-spotting or sheeting action, a need has arisen in the art for providing rinse compositions which can provide an effective stable source of active halogen such as chlorine.
In the past, the active chlorine has been incorporated directly into warewashing detergent formulations. However, the detergent environment reduces the effectiveness of the chlorine as a bleach or sanitizer and requires the use of large amounts of halogen for effective action. The pH of washing tanks using alkaline detergents is different than the optimum neutral pH range for bleaching. Further, the temperature in washing tanks is generally 20.degree.-40.degree. lower than optimal rinsing temperatures. The rate of bleaching reactions increases with increasing temperature and, all things being equal, chlorine is more active at high temperature. Lastly, the amount of organic soil load in the washing cycle is substantial. Chlorine attacks any organic species present. In the washing process, chlorine is then consumed by not only the microorganisms and stained ware but also by organic particulate food or non-food soil loads typically found in the wash tank. Therefore, the amount of solids present in the wash tank requires a significant increase in the effective concentration of chlorine required to accomplish destaining.
We have found that the efficacy of chlorine in destaining and sanitizing can be increased by introducing chlorine into the rinse cycle. Water used in rinse cycles is typically hotter, potable water at a relatively neutral pH. The entire concentration of active chlorine can then interact with stains on the surface of ware. Active chlorine at a concentration of about 3 to 50 ppm (depending on temperature) can provide destaining properties to a rinse aid and can typically be effective in removing even stubborn stains on ware derived from coffee, tea or other food sources. Higher concentrations of active chlorine (25 to 150 ppm) in rinse water can enable the aqueous rinse to kill sufficient numbers of microorganisms to fully sanitize ware during the rinse cycle (a 5 log.sub.10 kill is typically considered sufficient for sanitizing action). For the purpose of this application, available chlorine means free active chlorine species derived from the source of chlorine when the chlorinated solid rinse aid is mixed with water to form an aqueous rinse. Free active chlorine species are chlorine compounds that can chemically bleach and sanitize.
Copeland, U.S. Pat. No. 4,594,175 discloses sanitization can occur within the range of 50-100 parts of available halogen or chlorine per million parts of rinse composition applied in hot tap water (120.degree.-140.degree. F.) in the rinse cycle of the dish machine.
However, in developing chlorinated rinse aids, we have found that significant incompatibility problems have arisen in attempts to combine organic sheeting agents with active sources of halogen in powdered, liquid and solid materials. Rinse aids often contain polymeric moieties, derived from ethylene oxide, propylene oxide, or mixtures thereof, which are particularly sensitive to rapid oxidative degradation in the presence of halogen sources. The literature relating to the use of many organic substances in the presence of active chlorine indicates that the concentration of the organic substance in the final composition should be maintained at less than 10% and preferably less than 5% in order to maintain a high concentration of active chlorine in the final composition. Sedgwick et al, European Patent Application Publication No. 195619 discloses sanitizing destaining and rinsing processes and compositions discloses the use of peracid compositions in rinse aids because of their desire to avoid contacting an organic with an active chlorine source. 0n page 3 of the published application, Sedgwick discloses that "a further disadvantage is that chlorine-release agents cannot easily be included in the rinse additive that must in any case be injected into the rinse line and, therefore, two products are required to be injected into the final rinse water." Further drawbacks relating to the use of active chlorine sources are disclosed.
At significantly higher concentrations of functional organic materials (sheeting aids, surfactants, etc.), rapid reaction between the organics and the chlorine can deplete the concentration of both the functional organics and chlorine resulting in failure to either effectively promote rinsing and sanitizing or destaining. Further, the manufacturer of solid materials involved in contact between the halogen source and organic material at elevated temperatures can result in rapid oxidation which can produce substantial quantities of smoke and in some cases fire. The manufacturers of product data sheet for CDB-56.TM., an active chlorine product of Olin Chemical Corporation, states that contamination of the active chlorine material with an organic material may start a chemical reaction possibly resulting in fire or explosion. Such hazards substantially increase the difficulty of manufacture of these products.
Accordingly, a substantial need exists in the art for rinse aids and rinse aid concentrates containing an effective amount of organic surfactant to provide rinsing action and an effective amount of a source of active halogen to provide either destaining, sanitizing or both.